U.S. Scientists Creating Chimera Embryos For Organs: This Isn’t Your Mother’s Science Fiction

What do you get when you cross parts of a human with parts of an animal? Not a bad joke. Not even a line from the book The Island of Dr. Moreau. Not even a sci-fi character from Star Trek (although that’s closer). Scientists in the U.S. are pushing the limits of fiction into fact and testing the boundaries of ethics as they go, creating chimera embryos to “improve lives.”


Just as GMO foods were initially created from forcing DNA from two components together to form one unnatural item instead of finding them growing naturally in, well, nature, researchers have found yet another way to “play God,” according to some, combining human and animal DNA to create chimeras, hybrid embryos, in the interest of furthering science and to improve peoples’ lives.

“Chimera” is defined as “unreal,” a “mythological, fire-breathing monster, commonly represented with a lion’s head, a goat’s body, and a serpent’s tail,” as illustrated in the Iliad. However, Researchers at the University of California, Davis, are attempting to develop human-animal embryos for real, in order to grow organs that could help treat a wide range of human diseases.

The end goal of this “biomedical purpose” says Pablo Ross, a biologist at UC, Davis, is not “to see some kind of monstrous creature,” but to grow human organs inside farm animals to better understand human diseases and create better ways to treat them.

How it Works

To understand the scenario, first we have to understand that bio-engineering and gene engineering are not new ideas, and that this type of research and experimentation has been around for decades. Humans have received organs, such as heart valves, grown from pig and cow tissue before. One reason pig tissue is such a good material to use, explains the Genetic Literacy Project, is that “their hearts and other organs also have all of the crucial components of the extracellular matrix that makes up an organ’s scaffolding. But unlike human organs, the pig organs don’t tend to carry or transfer human diseases. That is a major advantage that makes them ideal starting material.”

Secondly, to understand the mechanics of the process, we must imagine a car. To make an old car new again, you remove the old parts—engine, transmission, other guts—and are left with the frame. You install brand new parts and you have new, updated innards within the same frame, and it will run for years to come.

The chimera concept, so to speak, from the medical/scientific angle, is to begin with a “frame” from, for example, a pig heart, clean out the heart’s old parts (a new, very effective procedure uses certain detergents), inject it with human stem cells from the patient recipient, and allow a new heart to grow which could then be transplanted into the human patient recipient. Because the organ was grown with that patient’s stem cells, the hope is this will reduce the “risk that the body would reject the new organ.” Researchers are hoping 3D printing will someday allow this to happen, but it’s not at that point yet.

Technical What-Not and Hope

With the chimera embryos, however, here’s where the gene-editing techniques and the ethical “but what ifs” come into play, NPR reported. Someone like Ross from UC, Davis, and his colleagues, takes a pig embryo and removes the gene that pig embryos need to make whatever organ researchers are trying for—this time let’s say it’s a pancreas for someone suffering from diabetes. This involves a microscope, a hole, and a laser.

A second hole is made and he injects human-induced pluripotent stem cells, or iPS, which are able to “turn into any kind of cell or tissue in the body.” The hope (meaning there is no guarantee whatsoever) is that the stem cells see the void from where the former pig pancreas gene was removed, and begin forming the human pancreas the researcher wants it to form.

The risk is that since these cells could form anything at all, they could even go to the brain of the embryo, which theoretically could result in a pig with a “consciousness like a human,” says Stuart Newman, a professor of cell biology and anatomy at the New York Medical College, which opens up a large can of ethical and moral worms.

But back to the chimera embryo: in order for the organ to form, the embryo must be implanted into an adult female pig womb, which Ross does surgically. He implants 25 at a time into more than one pig. The chimera embryos are only allowed to grow for 28 days which is when an embryo begins to form organs, and then it is removed and dissected to see exactly what the human stem cells were forming in there. Did they form the pancreas the researcher wanted? Did they start forming any other organs? Have they even formed human sperm or human eggs?

Eventually the goal is that “the body parts could then be harvested and transplanted” into terminally ill patients, but the unknown of what the stem cells could start forming is where the ethical controversies are springing up.

The Pesky Ethical Stuff

Although the scientific, medical, and biological potential does seem enormous, and the end goal of creating newer replacement parts to put into worn-out bodies, so to speak, sounds good at the outset, word of these experiments is spreading through the scientific and bioethical communities, and raising serious questions.

The National Institutes for Health (NIH) has halted funding on all chimera-based studies until the ethics involved can be studied. Questions that bypass the biological-ness of these experiments abound: If you are mixing animal and human, how much is human? How much is animal? How can you tell? Is there a certain percentage at which point a chimera embryo is considered more “human,” and does this then equate to growing human test subjects? They said they can guarantee there won’t be any mating, which “could give birth to some kind of part-human, part-pig creature,” but can they really?

The scientists and researchers involved are so determined to continue growing chimera embryos that they are not letting the halt in funding from the NIH deter them; they have simply found alternative funding sources such as the Department of Defense and the California Institute for Regenerative Medicine, hoping the NIH will see the positive results of their research and change their minds.

Do positive scientific results of growing human organs in chimera embryos outweigh any negative ethical issues that will arise? That remains to be seen. But this is certainly a fascinating area to keep an eye on to see what the NIH rules, and where experimentation goes from here.

[Photo by Seoul National University/Getty Images]